1. Field of the Invention
This invention relates generally to audio data storage formats, and more particularly to the physical format of audio data written to compact discs (CDs) in a compressed format.
2. Description of the Related Art
As is well known, the primary user of CDs is the music recording industry. An advantage of CDs is that data is digitally stored and end users are sure to get the same quality recording years after first purchasing the CD as when the CD was initially recorded. Although pre-recorded CDs are well received by consumers, with the advent of recordable CDs, such as, compact disc recordables (CD-Rs), users are quickly realizing that uncompressed data takes up a substantial amount of space.
By way of example, today many companies make audio titles available for sale over the Internet. Computer users therefore have a need to transfer downloaded music titles from their computer hard drives to, for example, a CD. However, most well known audio data recording applications record music in a format that does not allow for a large amount of music data to be recorded. As a result, users that want to store music titles onto a CD media have to use multiple discs to complete the task.
In view of the foregoing, there is a need for compressed audio data formats and techniques for writing the audio data formats onto a CD media. The compressed audio data format should allow for the storage of substantially more music data onto standard size CD media. Once recorded, the music data should be accessible by way of a standard computer system that communicates with a file system that provides access to the music data, or audio players having microcontroller hardware or software to directly access the compressed data stored on the CD media.
Broadly speaking, the present invention describes a format, method, and computer readable media for writing compressed audio data to a compact disc media. The writing of the compressed audio data includes the writing of a format that facilitates access to the audio data by a personal computer accessing a file system or a microcontroller based player. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium. Several inventive embodiments of the present invention are described below.
In one embodiment, a method for writing compressed audio data to a compact disc media is disclosed. The method includes selecting songs to be written in a session and reserving a first track. After the first is reserved, the method proceeds to writing a first temporary data structure and audio data to a second track following the first track. After the second track is closed, the first temporary data structure is written to the reserved first track and the session is closed. The writing of the first temporary data structure further includes writing an INFO.CD3 file in a first sector of the second track and writing a FILENIFO.LC file in sectors following the first sector of the same second track. Zeros are then written to fill-in a remainder of a sector containing at least part of the FILEINFO.LC file. In one specific example, the writing of the temporary data structure includes writing the INFO.CD3 file to a sector 15 of the first track, writing a file system (i.e., ISO 9660 File System) beginning at a sector 16 of the first track.
In another embodiment, a method for writing compressed audio data to a compact disc media is disclosed. The method includes beginning a session writing the compressed audio data to the compact disc media. A track includes a file system followed by an audio data section. The writing of the file system includes writing an INFO.CD3 file and an ISO 9660 file system. Once the track is written, the method proceeds to closing the track and closing the session. In this preferred embodiment, the INFO.CD3 and FILEINFO.LC files define a microcontroller system structure (MSS) that is independently accessible to a microcontroller-based player.
In yet another embodiment, a computer readable media having program instructions for writing compressed audio data to a compact disc media is disclosed. The operations of the computer readable media include program instructions for selecting songs to be written in a session and program instructions for reserving a first track. Once the first track is reserved, the computer readable media includes program instructions for writing a first temporary data structure and audio data to a second track following the first track. Then, program instructions are provided for closing the second track and writing the first temporary data structure to the reserved first track. In this embodiment, when the first temporary data structure is written to the reserved first track, the writing of the first temporary data structure includes program instructions for writing an INFO.CD3 file and an ISO 9660 file system to the reserved first track. Program instructions then follow to close the session.
In still another embodiment, a computer readable media having program instructions for writing compressed audio data to a compact disc media is disclosed. The operations of the computer readable media include: (a) program instructions for beginning a session writing the compressed audio data to the compact disc media; (b) program instructions for writing a track including a file system and an audio data section. The writing of the file system further includes: (i) program instructions for writing an INFO.CD3 file; and (ii) program instructions for writing an ISO 9660 file system. The computer readable media then includes: (c) program instructions for closing the track; and (d) program instructions for closing the session.
In a preferred embodiment, during the writing of a CD3 music CD, a session can be written at once or during separate multiple times. When the CD3 music CD session is written at one time, the CD is preferably written in the form of only one track that contains an ISO file system 302 and audio files data 124b (e.g., see FIG. 8A). When the CD3 music CD session is written during different record phases, it will contain at least two or more tracks; one for the file system information and one or more for the data.
As will be discussed below, the CD music CD session can contain more than one data track that is written during different recording phases. In this case the session is preferably formatted with the first track reserved for the ISO 9660 file system, which has a length of 300 Kbytes or more. Each data track will contain a temporary data structure (TDS) that includes microcontroller data structure information for the construction of the file system when the session is closed (e.g., INFO.CD3+ FILEINFO.LC files).
When the session is written in the incremental way, at least 2 tracks are required in the session: one for the file system and one for the data track. The file system track contains the ISO 9660 file system structure and at minimum the INFO.CD3 file. The INFO.CD3 file is written at a relative sector address 15 of the first track of the current session. Of course, any other sector can also be used if modifications are made to the CD3 specification defined herein. The current track is reserved before the first data track is written. The track can have a variable length with a minimum of 300 Kbytes, in this embodiment. The ISO 9660 file system and INFO.CD3 are written just after last data track is written and before the current session is closed as will be described with reference to FIG. 5. In a further embodiment, if the file system structure is bigger than the current file system track length, a new file system track will be written at the end of the last data track. In this example, the file system will be written in the last track, while the INFO.CD3 structure and PVD will be written in the first file system track.
With regard to reading the CD3 music data, a CD3 music CD disc preferably contains one type of data retrieval structure, which is advantageously compatible to different types of playback systems. For example, one type of playback system is by way of the file system structure (FSS) that preferably conforms to the CD-ROM XA specification. Another is by way of the microcontroller system structure (MSS). The MSS is intended for microcontroller-based playback systems, which can be in the form of a CD3 player. CD3 players can be part of an automobile audio CD player, a home CD player, a portable CD player and the like.
The file system structure (FSS) and the microcontroller system structure (MSS) of a session give independent access to all the data on the disc from the first session up to and including the current session.
The file system structure (FSS) allows personal computers to retrieve and play audio files accessing the files in the DATA directory. The direct access to the relative sector address 15 of the current session allows microcontroller-based playback systems to retrieve all the information needed to play the audio files.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.